Process for the production of aromatic and olefinic hydrocarbons



Nov.[24, 1970 J. F. M cMAHoN L-:TALl 3,542,667

Y* PROCESS FOR THE PRQDucTIoN or' AROMATIC AND oLEFINIc HYDRocARNs Filed 'March `21, 1,968

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PROCESS FOR THE PRODUCTION OF 'AROMATIC `AND OLEFINIC HYDROCARBONS Filed Mar'h "21, 1968 2 Sheets-Sheet 2 w al@ M .k m 8 6 4 2 0 /f/ /l E .n m. .c. y w mm .muww W ,/Qf d MM o n. l v cl] asie /J ,m88 Cr 83 wwe sP.cc A a CF aa A .QDwP No P0. e .6 s dass V Y m c uw w. y?. i?, CV 4M 64M ma. n/..../. u 0 .3.4. man N 44 `0 u ,OLP 0` ../o. Mmgk m. 8 5 4` 2 0 TEMPERATURE, F

PYROLYSIS -CUTLET m. .mw mN. @m ma l l go VHS T NATM COM MPAH 0 T ELEM7 MJGD Us. cl. 20s- V66 United States Patent O Joseph F. McMahon, Clinton, and John J. LoPorto, Brookside, NJ., and George F. Adams and Dana L. Smith, Tulsa, Okla.; said McMahon andsaid LoPorto assignors 'to Foster Wheeler Corporation, Livingston, `NJ., a corporation of New York; said Adams and said Smith assignors to Sun Oil Company, Tulsa, Okla., a corporation of New Jersey Filed Mar. 21, 1968, Ser. No. 714,869

` Int. Cl. C10g 23/00 14 Claims which can be separated from the aromatics by simple distillation.

The present invention relates to a process for obtaining from a naphtha feed stock two valuable products,

an aromatic product including benzene and toluene, and an olefin product, primarily ethylene.

lNaphtha is a fraction obtained from crude distillation -of virgin petroleum oil. It boils in the gasoline range of approximately 150-400 F., and is a low value product,

but often useable as a source of hydrocarbons. Hereto- Afore, the general practice has been to process naphthas Vcontaining a high proportion of parains to obtain a high olen yield, since an increased aromatic content was fusually associated with a decreased olenic yield. In accordance with the present invention, it was discovered -that a highly aromatic naphtha could be successfully -processed to produce valuable products,- and in fact, for -fpurposes of the present invention, the naphtha should ybe naphthenic in character containing a quantity, up to 5%, and preferably 30 to 50% naphthenes, as precursors of benzene and other aromatics. The remainder of the naphtha is aliphatic, primarily straight-chain parains.

A known process for producing both ethylene and ben- "zene from-naphtha includes the step of subjecting the naphtha Afeed stockito reforming, followed by solvent extraction of Aaromatics from the reformate. The reforming which may be carried out at about 900 F. in the presence of a catalyst and at a pressure between 100 and 600 p.s.i. produces a high yield of high octane reformate in which the cyclic naphthenes are converted to Athe aromatics. In the Asolvent extraction step, a suitable solvent such as diethylene g'lycol extracts aromatics form `the reformate leaving a parafnic raffinate suitable for subsequent treatment. Solvent extraction is necessary, as

`simple distillation Vis impossible in view of the closeness `of the boiling points of the aromatics and high boiling non-aromatics at this stage. Following solvent extrac- -"tion, the aromatics recovered from the solvent are subjected to hydrodealkylation to produce benzene. Paratlins in the rainate phase are pyrolized under high severity cracking conditions to produce ethylene. A principal problem of this known process is that the solvent extraction step is di'icult and expensive but is necessary to separate the high molecular weight non-aromatics from the aromatics to obtain a relatively pure aromatic rstream.

3,542,667, Patented Nov. 24, 1970 A second method for obtaining benzene and ethylene from a naphtha feed stock includes first subjecting the naphtha to pyrolysis in the presence of steam, at a high temperature, and in the absence of a catalyst to crack the long chain aliphatics to ethylene. The pyrolsis is followed by hydrotreating, solvent extraction to produce an aromatic rich extract, and hydrodealkylation of the aromatics to yield benzene.` In the pyrolysis step, the straight chain single bonded parains are cracked to the double bonded olefns, and the naphthenes are partly converted to aromatics. However, there occurs in the lpyrolysis reaction undesirable side reactions including cracking of the naphthenes with resultant loss of product, and only partial removal of paraiiins from the boiling range of the aromatics formed, necessitating the solvent extraction step. l f

Accordingly, this second method suffers from the same disadvantage as the previous method mentioned above, namely the expense of solvent extraction. In addition, there is the loss of valuable cyclic compounds reducing the benzene yield. In this respect, the pyrolysis step causes a cracking of naphthenes particularly if the conditions are severe enough to obtain a high degree of removal of paraflins from the boiling range of the aromatics formed.

In accordance with the present invention, it was discovered that the disadvantages of the prior methods could be avoided by subjecting the reformate from catalytic reforming directly to pyrolysis under such conditions as to avoid destruction of cyclic compounds and at the same time achieve a reduction in molecular weight of the aliphatics such as to permit removal of nonaromatics by simple distillation or fractionation methods.

In particular, the present invention comprises the steps of catalytically reforming a naphtha fed stock (wherein the cyclic naphthenes are converted to aromatics), then subjecting the liquid reformate to pyrolysis or cracking in the presence of steam at high severity conditions so as to produce a highly aromatic liquid and a gaseous oleinic stream. Ethylene is produced from the latter, and the aromatic liquid stream is subjected rst to hydrotreating, and then simple distillation to remove separate butane and pentane cuts, leaving substantially pure aromatic stream from which benzene can be produced. The essence of the present invention is the discovery that a reformate stock could be subjected to cracking under such conditions as to avoid destruction of cyclic compounds, but at the same time reduce the molecular weight of the aliphatics to that which permits their separation from the cyclic compounds by simple distillation or fractionation methods. The pyrolysis is severe, being carried out at a temperature in the range of 1300 F. to 1700 F., with an outlet temperature which preferably is in the range of 1450 F. to 1550 F., a preferred residence time between about 0.24 and about 0.60 second, and preferably a steam to hydrocarbon weight ratio of from zero to about 4.0.

It will become apparent upon further reading of the following specification that the present invention achieves a higher aromatic yield than that heretofore achieved, and eliminates the solvent extraction step heretofore required.

VThe invention and advantages thereof will become apparent upon further consideration of the speclcation with reference to the accompanying drawings, in which:

FIG. 1 is a flow diagram illustrating the method in accordance with the invention, including those steps to produce benzene; and,

FIG. 2 is a graph showing pyrolysis conditions illustrating the concepts of the invention.

Referring to the gures, virgin petroleum naphtha obtained by crude distillation of petroleum oil, boils in the gasoline range of 150 to 400 F. and contains more than 5% naphthenic compounds preferably 30 to 50% naphthenes. This naptha is introduced in line 12 to a desulfurization reactor 14, which is conventional, followed by cooling and HZS removal (item 16). The naphtha is then preheated, in heater 18, and is contacted in vessel 20 with a reforming catalyst such as platinumalumina, or chromia-alumina, in the presence of hydrogen introduced in line 21 so that a substantial part of the naphthene compounds in the virgin naphtha are converted to aromatic compounds. The reforming step is carried out at a temperature in the range of 600 F. to 1000 F., at a pressure in the range of 0 to 1000 p.s.i., and at a hydrogen to hydrocarbon ratio, s.c.f.b. (standard cubic feed per barrel) in the range of to 10,000. The process to this point is conventional, particular conditions being dictated by the type feed involved, catalyst used, and products desired.

The hydrocarbon reformate from the reforming step is condensed in cooler 22, is separated in separator 23 from hydrogen product gas ,(which may be recycled to the naphtha feed stream via line 21), and is then reheated in heat exchanger 24. Recycle low molecular weight hydrocarbons, for instance C olens from a later cut (to be described) in line 26 are mixed with the hydrocarbon effluent, as is stream, in line 28, and the mixture is then subjected to high severity (high temperature) pyrolysis cracking in heater 30. Preferred pyrolysis conditions are a temperature in the range of 1300 to 1700 F., with outlet temperatures in the range of 1450 to 1550 F., preferably 1500 F.; a pressure in the range of 0 to 60 p.s.i.g.; a steam to hydrocarbon weight ratio of 0.1 to 2.0 (about 0.5 to mols of steam per mole of hydrocarbon); and a contact or residence time in the pyrolysis zone in the range of 0.05 to 1.0 second, preferably between 0.24 and 0.60 second. In this latter respect, it was found that the pyrolysis or cracking of the aliphatics was not materially affected by differences in throughput, but that the loss of C5 ring compounds 'was affected, the loss increasing with a decrease in throughput or increase in residence time.

The results of the cracking step can be understood by consideration of the effluent streams from quench tower 32, the gaseous pyrolysis product being subjected to quench in a conventional manner l(construction of such a tower and quench conditions are well known). From the quench tower 32, there are three product streams, an overhead gas stream in line 34 heading from the top of the tower 32, an intermediate side liquid stream or fraction in line 36, and a -bottom product in line 37. The overhead stream or pyrolysis gas is primarily ethylene the conditions of pyrolysis causing cracking of the high boiling point long-chain aliphatics to the lower molecular weight lower 'boiling point double bonded olens and some diolefins. These components are readily separated from the rest of the pyrolysis effluent in the quench tower 32. The intermediate liquid steam or fraction of line 36 boils in the range of 169 F. to 350 F. and contains the bulk of the aromatics, which as mentioned, have been virtually unaffected in the pyrolysis step (in a subsequent example, it will be shown that a 90% or higher recovery of C5 ring compounds in the feed can be achieved, indicating little destruction of cyclic compound in the pyrolysis step), and some C4 and C5 butane cuts to be described. A heavy 350 F. plus steam primarily cyclic compounds may be withdrawn from the bottom of the quench tower.

The hydrocarbon pyrolysis liquid line 36 from the quench tower 32 (it has been mentioned that this stream boils in the range of 169 F. to 350 F.) may be subjected to mild hydrotreating conditions in reactor 42 in which small quantities of olefinic and diolenic compounds are hydrogenated to the corresponding parafnic compounds without effecting hydrogenation of aromatic rings contained in the liquid. This is a well known step, and the C., and C5 hydrogenated hydrocarbons can then be easily and readily fractionally distilled from the C5 ring compounds in the towers 38 and 40 to produce an aromatics rich fraction in line 44 boiling in the range of F. to 350 F. Pentane and 'butane cuts are obtained in lines 46 and 48 respectively, and the pentane cut `(line 46) can then be recycled to line 26, mentioned above. This is for the purpose of making more ethylene in the pyrolysis reaction, increasing ethylene yield, the pentane being pyrolyzed to ethylene under the conditions in the furnace 30.

Alternately, the pyrolysis hydrocarbon liquid from the quench zone, in line 36, can be fractionally distilled to produce an aromatics-rich fraction boiling between 150 F. and 350 F. which contains benzene, toluene, xylenes and other monocyclic aromatics, with subsequent treatment of olefins and diolens in the pyrolysis liquid effluent.

The pyrolysis gas stream (line 34) containing ethylene, propylene, butadiene and other light olens is sent to suitable recovery apparatus for the treatment of the pyrolysis product gas by conventional methods and recovery of ethylene.

For the recovery of benzene, the aromatics-rich fraction in line 44 may be sent to conventional dealkylation reactor S0 wherein methyl groups and other side chains are removed from C, and C8 aromatics to produce a benzene product. This is carried out in the presence or absence of a catalyst, usually at a temperature of 1000 F. to 1300 F., a pressure in the range of 200 to 1000 p.s.i. and at a hydrogen to hydrocarbon mole ratio in the feed of about 1 to 10. Stabilizer 56 and benzene tower 52, both simple distillation towers, complete the benzene recovery apparatus.

The pyrolysis reaction is more clearly illustrated with reference to FIG. 2. This graph shows in curve A the variations with outlet temperature of non-aromatics essentially C5 and higher in the pyrolysis liquid stream following the pyrolysis reaction, quenching, and simple fractionation in vessels 38 and 40; reflecting, in other words, the percent non-aromatics remaining after pyrolysis which are so close in boiling point to the aromatics that they were not separated from the aromatics by fractionation. The space velocities are lbs./hour/cu. ft. at about 15 p.s.i.g. outlet pressure. The graph also shows in curves B and C variation in loss of C6 ring compounds with pyrolysis outlet temperature, the data of curve C being obtained at a space velocity in the range of 141 to 148, and that of curve B being obtained at a higher space velocity (lower residence time) of 433 to 442. Referring first to curve A, it is apparent that at low outlet temperatures, for instance 1400 F., there will be clearly a substantial percentage of non-aromatics remaining in the pyrolysis liquid stream, indicating that there was little cracking of the higher boiling point aliphatics (C5 and higher). Because of the molecular weight of these aliphatics, they could not be removed by simple separation in quench tower 32, or even by simple distillation in fractionation towers 38 and 40, and the solvent extraction of prior methods would have to be resorted to in order to obtain a substantially pure aromatic stream. As the pyrolysis outlet temperature is increased, up to 1450 F., the percent non-aromatics C5 and higher remaining drops to 12%, and at 1500 F., to about 3%. At 1550 F. outlet temperature, the percent remaining is about 1%. An increase in temperature or severity of pyrolysis causes a reduction in the molecular weight of the non-aromatics and for the purpose only of removal of the non-aromatics by simple distillation, an outlet temperature between 1550 F. and 1600 F. is most desirable.

However, referring to curve B, the loss of C5 ring compounds by cracking, is substantial at temperatures above 1550", dropping to about 3% loss at 1500 F., and

1% loss at 1450 F. Superimposing the curves B and C, it is apparent that the temperature 1500 F. is most ideal towards achieving the purposes of the invention. Temperatures substantially above and below this temperature effect either too great a loss of cyclic compounds, or too little cracking of aliphatics.

FIG. 2 also shows that the cracking of the aliphatic compounds is not affected by throughput or space velocity (SV) (forinstance, at Y1500'? P. the percent non-aromatics remaining following the distillation steps of 38 and 40 is about 3% at space velocities of both 148 and 442), although the loss in C6 ring structure compounds is affected, being higher at the lower space velocity of 148 (curve C) as compared to a space velocity of about 442 for curve B. Accordingly a preferred space velocity is in the order of 442 lbs./hour/cu. ft. (about 0.24 second) although a 10% loss of aromatics is not excessive, and a contact time of about 0.60 second (148 lbs./hour/cu. ft.) is within the scope of this invention.

Although a preferred range of 0.1 to 2.0 was given for the weight ratio of steam to hydrocarbon for the pyrolysis reaction, the steam is added for the purpose of reducing partial pressure of hydrocarbons, and lesser amounts of steam could be used, including no steam, by using different operating conditions, for instance operating at a vacuum. Higher weight ratios, up to four could be used, although 2.3 seems to represent the present economical upper operating limit. Also, inert gases such as nitrogen and carbon dioxide could be used in place of steam.

With reference to contact time, 0.10 second at the present time seems to represent the lower practicable limit, as it seems impossible to build a tubular furnace for a lesser contact time.

-With reference, to operation of the quench tower 32, it is sufcent simply to mention that in one suchV design, the hot gas is admitted at the bottom of the tower, and spray quench water at the top. Trays near the middle of the tower collect the condensed 169-350 F. liquid, controls in the tower controlling the flow of quench water to maintain this temperature level on the collecting trays.

v Examples in accordance with the invention are as follows.

' EXAMPLE 1 A virgin Mid Continent naphtha having the following characteristics: l

was catalytically reformed by contacting the oil with a platinum containing catalyst in the presence of hydrogen. Liquid product recovered from the reforming operation, containing roughly 49 weight percent aromatics and 10.5 weight` percent C6 to C8 naphthenes, was'blended with 4 volume percent pentane (line 26) to obtain a catalytic -reformate of the following characteristics:

Gravity, API 49.8 ASTM boiling range:

IBPv 152 10% 186 50% 223 90% 279 EP 335 Component analysis: Wt. percent Benzene i 6.9 Toluene 19.4 Ethylbenzene 2.9 p, m-Xylene 12.2 o-Xylene 5.4 1,2,4 TMB 1.1 Unidentified aromatics 0.5 Heavy aromatics 0.7

Parans:

C5 3.1 C6 10.5 C7 9.8 C8 A1.1 C-l- 15.9

Naphthenes:

C5 0.1 C6 5.2 C7 4.6 C8 0.6

The analysis indicates a substantial conversion of cyclic naphthenes to aromatics.

The above described catalytic reformate was vaporized, mixed with steam in a weight ration of 0.78 lb. steam per pound of oil, and the mixture preheated to a temperature of 1200 F. The preheated mixture was passed through a steam pyrolysis coil which was contained in a heater red with natural gas.

The heater tubes were '1/2 inch Incoloy Schedule 40 pipe forming a series of loops in a vertical plane of the lirebox. The furnace was divided into four zones separated by refractory bridge walls. The first zone contained a steam coil and a preheater coil connected in series. The last three zones were reaction sections in which pyrolysis of hydrocarbons occurred.

The mixture of vaporized water and hydrocarbon is preheated to 1200 F in the preheat zone. In the remainmg zones, process fluid temperatures werecontrolled to establish a rising temperature profile in which the rate of temperature rise was highest in the rst reaction zone and lowest in the last reaction zone, typical profiles being:

Inlet to 1st reaction zone 12(5). Inlet to 2nd reaction zone 1440-1450 Inlet to 3rd reaction zone 1480-1520 Coil outlet temperature G-1550 Typically, pressure at the outlet was about 15 p.s.i.g. with pressure drop across the three sections varying from 2 to 15 p.s.i.g.

In this example, flow rate of the catalyticreformate was 442.0 lbs. of oil per hour per cubic foot of coil volume. The oil-steam mixture left the pyrolysis coil at a temperature of 1503 F. and a pressure of 14.8 p.s.i.g. Eluent from the pyrolysis coil was cooled to a temperature of about 750 VF. immediately after leaving the heater. Product vapors were then cooled to 60 F. with water and refrigerant. Pyrolysis liquid product and water were separated from gaseous product in the liquid accumulator. The following product yields and product qualities were obtained based on analysis of gaseous and liquid streams:

Product yields, wt. percent feed:

Ethylene 15.4 Propylene 8.7 Butadiene 2.3 Benzene 7.4 Toluene 18.1 Xylenes 13.3 Styrene 4.3 Percent recovery of C6 aromatic rings 97.0

Percent non-aromatics in 169-350 F. pyrolysis liquid EXAMPLE 2 The catalytic reformate described in Example l was vaporized, mixed with steam in a weight ratio of 0.77 lb. steam per pound of oil and the mixture preheated to a temperature of 1200 F. The preheated mixture was passed through the steam pyrolysis coil at a ow rate of 433 lb. of oil per hour per cubic foot of coil volume. The oil-steam mixture left the pyrolysis coil at a temperature of 1553 F. and a presure of 15.4 p.s.i.g.

Gaseous and liquid products were recovered as described in Example 1 and analyzed. The following results were obtained.

Product yields, wt. percent feed:

Ethylene 17.1 Propylene 8.1 Butadiene 2.0 Benzene 8.0 Toluene 18.2 Xylenes 10.7 Styrene 3.8 Percent recovery of C6 aromatic rings 92.0

Percent non-aromatics in 169-350 F. pyrolysis liquid EXAMPLE 3 The catalytic reformate described in Example 1 was vaporized, mixed with steam in a weight ratio of 0.75 lb. steam per pound of oil and the mixture preheated to a temperature of 1200 F. The preheated mixture was passed through the steam pyrolysis coil at a iiow rate of 148 lb. of oil per hour per cubic foot of coil volume. The oil-steam mixture left the pyrolysis coil at a temperature of 1502 F. and a pressure of 15.0 p.s.i.g.

Gaseous and liquid products were recovered as described in Example l and analyzed. The following results were obtained.

Product yields, wt. percent feed:

The catalytic reformate described in Example 1 was vaporized, mixed with steam in a weight ratio of 0.81 lb. steam per pound of oil and the mixture preheated to a temperature of 1200 F. The preheated mixture was passed through the pyrolysis coil at a ow rate of 141 lbs. of oil per hour per cubic foot of coil volume. The oilsteam mixture left the pyrolysis coil at a temperature of 1551e F. and a pressure of 15.0 p.s.i.g.

Gaseous and liquid products were recovered as described in Example l and analyzed. The following results were obtained.

Product yields, wt. percent feed:

Ethylene 17.5 Propylene 5.9 Butadiene 1.4 Benzene 12.2 Toluene 16.2 Xylene 6.4 Styrene 2.5 Percent recovery of C6 aromatic rings 89.0

Percent non-aromatics in 169-350 F. pyrolysis liquid The following residence times are equivalent to the aforementioned space velocities given in the above examples, for the pressures and temperatures used.

Residence time,

Space velocity, lbs./hr./cu. ft.: seconds 442 0.25 433 0.24 148 0.60 141 0.59

The examples and other experiments carried out in accordance with the invention showed that at about l500 F., coil outlet temperature, the yield of ethylene varied between 15 and 17 weight percent of feed at contact times of 0.24 to 0.60 second. At 1550 F., coil outlet temperature, ethylene yield was approximately constant at 17 weight percent of feed over the same range of contact time. Reduction in steam to hydrocarbon ratio from 0.8 to 0.55 at the higher temperature reduced ethylene yield from 17.3 to 16.5 weight percent.

Although the concepts of the invention are applicable to parainic naphthas a-s well as aromatic naphthas, results showed that yields of ethylene, propylene, methane and butadiene from aromatic naphtha may be as little as 50% of the corresponding yields obtained from parafnic naphthas. A typical paraflnic naphtha is natural gasoline boiling between and 305 F., ASTM and containing 96.9% parains, 1.6% naphthenes, and 2.5% aromatics by weight. Because of the effect of aromatic content of naphtha on ethylene yield, the inventions primary use probably is with naphthas containing from 30 t0 50% naphthenic compounds.

Analysis of the liquids produced in experiments provided data on the effect of operating conditions on yield of benzene, toluene, xylene, and styrene, particular conditions considered being outlet temperature and residence time. Xylene yields include the 3 isomers and ethylbenzene. Correlation curves were drawn so that yields at zero contact time corresponded to the feedstock composition.

At 1500 F., outlet temperature, xylene yield decreased from 20.5 weight percent of feed at zero contact time to 8 weight percent of feed at 0.6 second contact time. Toluene yield decreased from 19.6 weight percent to 17 weight percent and benzene yield increased from 7 to l1 weight percent over the same range of residence times. Styrene yield reached a maximum of 4 weight percent at 0.25 second contact time and then decreased at longer residence times. Maximum styrene yield was about 30% higher than the concentration of ethylbenzene in the feedstock.

At 1550 F., coil outlet temperature, the effects of contact time on benzene, toluene, Xylene, and styrene yields were similar to those observed at 1500" F., temperature. Xylene, toluene, and styrene yields were slightly lower and benzene yield was slightly higher at comparable contact time. A decrease in steam hydrocarbon ratio decreased xylene yield and increased benzene, toluene and styrene yields. The net effect of pyrolysis on the Cs-Cs aromatics present in the naphtha feed was primarily to 93. increase benzene concentrationvand -decrease xylene concentration. Toluene concentration tended to remain relatively constant.

The observed yields of Cs-Ca aromaticsobtained from the pyrolysis of aromatic naphtha appear to bethe net result of `several thermal reactionsLThese reactions include the formation of aromatics from the parafn-naphthene portioa ofthe` feed,fdealkylati`n of aromatics', and cracking or polymerizationnof aromaticcompounds to lower and higher boiling products. The net yield of benzene, toluene, xylene, and styrenewas compared to the concentration of benzene, toluene, xylene and ethylbenzene in the feedstock on the basis of contained C6 rings. The C6 ring recovery is independent of changes in weight yields due only to alkylation-dealkylation reactions. The C6 ring content of the feed was 38.3 weight percent based on CG-CB aromatics.

Recovery of C6 rings at 1500 F., outlet temperature decreased from 94% at 0.25 second contact time to 87% at 0.6 second contact time. At 1550 F., outlet temperature C6 ring recovery varied from 91% to 85% over the same range of residence times. A decrease in steam to hydrocarbon ratio from 0.8 to 0.55 increased C6 ring recovery at 1550 F., outlet temperature. This result was presumably due to increased formation of aromatics from the parai'linic and naphthene components of the feedstock.

It is apparent that the present invention resides primarily in the discovery that an optimum pyrolysis condition exists which results in suficient pyrolysis of nonaromatics with minimal loss of aromatics.

The advantages of the process of this invention arise from the fact that an aromatics-rich liquid is produced directly from the pyrolysis step of the process thereby eliminating the need for extraction to separate parains from aromatics. The process of this invention requires less processing equipment than conventional methods which require extraction. In addition the process of this invention provides higher yields of aromatics or benzene than conventional processes in which virgin naphtha is subjected directly to pyrolysis conditions without prior catalytic reforming, in that the naphthenes in the feedstock are less able to withstand the rigors of pyrolysis than the aromatics of the pyrolysis feedstock of the present invention. By the same token, since the stream entering the pyrolysis furnace in the present invention is aromatic, the severity of cracking can be greater producing a higher purity benzene or aromatic yield.

Although the invention has been described with reference to specific examples, variations within the scope of the following claims will be apparent to those skilled in the art.

What is claimed is:

1. In a process for the production of aromatics, olens and diolens from a naphtha feed stock, which process includes the steps of catalytically reforming the stock in the presence of a catalyst under such conditions as to convert naphthenes in the feed stock to aromatics, subjecting the reformate to pyrolysis, and quenching the pyrolysis eiuent, the improvement comprising:

using a naphthem'c feed stock containing at least 30% naphthenes;

pyrolizing the reformate at a coil outlet temperature in the range of about 1450 to about 1550 F. with a residence time of between about 0.10 seconds and about 0.60 seconds whereby the long chain aliphatics are converted to lower molecular weight oleiins and dioleiins;

the quenching being for a sufficient time and at such temperature as to produce a gas stream which is predominantly ethylene, and a liquid side stream which boils in the range of about 169 F. to about 350 F. and is primarily aromatic.

10 2. A process according to claim 1 wherein substantially all of 'the' non-aromatic content of said liquid stream consists of parains of C5 or less. y3. Afprocessaccording to claim 2 further including the step of subjecting the quenched liquid stream to simple fractionation to separate the C5 and lighter paraius from the aromaticsto produce a substantially pure aromatic stream boiling inthe range of vabout 150` F. to about 350 F.

f4. A' process according to claim 3 wherein said liquid stream further contains a small amount of olefinic and diolenic compounds, said process furtherincluding the step of hydrotreating said liquid stream prior to said fractionation step to hydrogenate the oleiinic and dioleinic compounds therein to the corresponding paraiinic compounds.

5. A process according to claim 1 wherein said residence time is at least about 0.24 seconds.

6. A process according to claim 5 wherein the steam to hydrocarbon ratio in the pyrolysis step is in the range of about 0.1 to 2.3.

7. A process according to claim 5 including the step of preheating the reformate to a temperature of about 1200 F. prior to pyrolysis, the pyrolysis reaction being carried out at increasing temperatures in the range of about 1200 F. to about 1550 F.

8. A process according to claim 7 wherein the pyrolysis is carried out in three separate heating zones, in series, the temperature of pyrolysis being maintained below incipient cracking temperature in the first two of the three zones and outlet temperature being in the range of l500 1550 F.

9. A process according to claim 5 wherein the gas inlet temperature prior to quenching is about 400 F., the gas stream temperature following quenching being about 100 F.

10. A process according to claim 5 wherein coil outlet pressure in the pyrolysis step is about 15 p.s.i.g.

11. In a process for the production of aromatics, olefins and dioleiins from a naphtha feed stock, which process includes the steps of catalytically reforming the feed stock in the presence of a catalyst under such conditions as to convert naphthenes in the feed stock to aromatics, subjecting the reformate to pyrolysis, and quenching the pyrolysis effluent, the improvement comprising:

using a naphthanic feed stock containing from about 30 to about 50% naphthenes;

pyrolizing the reformate at a coil outlet temperature in the range of about l450 F. to about 1550 F. with a residence time of between about 0.24 and about 0.60 second, whereby the long chain aliphatics are converted to olens and dioleiins;

the quenching being at such temperature and for a sufficient period of time to produce a gas stream which is predominantly ethylene, and a liquid stream which boils in the range of about 169 F. to about 350 F. and is primarily aromatic, the liquid stream representing a recovery of at least about C6 ring compounds in the feed stock.

12. A process according to claim 11 including the steps of hydrotreating the pyrolysis liquid stream under such conditions as to hydrogenate oleiins and dioleiins therein to corresponding paraflinic compounds; and

fractionating the hydrogenated liquid stream to remove the paratfns therefrom;

the non-aromatics remaining therein being less than about 2.7%.

13. The process according to claim 11 wherein the pyrolysis conditions are as follows- Range of reaction temperatures: 1200 F. to 1700 F.

Pressure range: 0 p.s.i.g. to 60 p.s.i.g.

Steam to hydrocarbon ratio: 0.1 to 2.3

the process further including the steps of hydrotreating the liquid stream to convert oleiins and diolefins therein to corresponding parains;

1 1 subjecting the hydrotreated liquid stream to simple fractionation to separate C4 and C5 hydrocarbon cuts from the aromatics to produce an aromatic stream boiling in the range of about 150 F. to about 350 F. and comprising more than about 97% aromatics; and recycling the C5 hydrocarbon cut to the reformate stream for pyrolysis thereof and production of additional ethylene. 14. The process of claim 11 wherein the naphtha feed stock boils in the gasoline range of about 150 F. to about 400 F. and is prepared by distillation of crude oil.

References Cited UNITED STATES PATENTS DELBERT E. GANTZ, Primary Examiner A. RIMENS, Assistant Examiner U.S. C1. X.R. 208-62g 260-683 

